SITE INFORMATION AND CORRESPONDENCE

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Ms. Wendy Wyels Page Two September 15, 1993 In addition to delineating the lateral and vertical extent of TKN contamination, hand augering will be used to document the depth to ground water at several locations at the project site. The first saturated zone is believed to be at 10.5 feet below the surface. Reliable ground water level data is essential to estimate soil volumes and efficiently remove contamination. 2. MONITORING WELL (MW-1) ABANDONMENT - A ground water monitoring well (MW-1) was installed at the Washington Street site in 1991. A ten-inch boring was advanced until first water was encountered at a�u� 201 z t. Th_- boring was then advanced to 35 feet. Soil samples were taken by the split-spoon method at five- foot vertical intervals. A four-inch PVC casing was positioned and well screen installed from 3.5 to 33.0 feet (Mittlehauser, 1992). After development of the well, the water level reportedly stabilized at about 13 feet. In May 1993, Sierra-Pacific measured the water level at 10.5 feet below the top edge of the PVC casing. Testing indicates that monitoring well MW-1 was advanced through a zone of urea- contaminated soil. Urea-contaminated soil may extend to the saturated zone, which is 10.5 feet below the surface. Thin dark-colored clay beds were identified during Sierra-Pacific's Spring 1993 soil sampling program. Other, relatively impermeable, clay beds may exist within the 20 to 30-foot soil interval. Monitoring well MW-1 is screened from 3.5 to 33.0 feet, and may provide a man- made conduit for ground water movement. MW-1 should be over-bored, grouted, and decommissioned prior to excavation of urea-contaminated soil at the site. 3. MONITORING WELL INSTALLATION - Installation of four new monitoring wells be undertaken carefully to avoid penetrating impermeable clay beds which may exist within the 1.0 to 20 foot depth interval. A laterally-continuous clay bed, positioned correctly, could prevent downward migration of TKN constituents and thereby limit the extent of ground-water contamination. A monitoring well installation workplan is being prepared. The proposed location of the new wells is shown on the attached figure. 4. GROUND WATER MONITORING - New monitoring wells will be measured to determine ground water flow direction, then sampled and tested to document any presence of TKN in the groundwater. 5. DEMOLITION, EXCAVATION AND SOIL REMOVAL - Several aboveground storage tanks, pipes, and fittings may have to be removed from the site. Unocal estimates that more than 1000 tons of urea-contaminated soil may have to be • excavated and removed. The volume of soil and concrete requiring remediation or